Image sensor

ABSTRACT

An image sensor, in which, a planarized layer is formed on a semiconductor substrate including a pixel array region, an optical black region, and a logic region to cover a photo sensing unit array in the pixel array region, a patterned metal layer is formed on the planarized layer corresponding to the pixel array region and the logic region, but not the optical black region. An optical black layer is formed in the optical black region after a passivation layer is formed and before a color filter array is formed at a temperature less than about 400° C., and preferably contains metal material.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a divisional application of U.S. patent application Ser. No.11/461,457 filed on Aug. 1, 2006, and the contents of which are includedherein entirely by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image sensor and a method ofmanufacturing the same, and more particularly to, a CMOS image sensorand a method of manufacturing the same.

2. Description of the Prior Art

CMOS image sensors (CISs) and charge-coupled devices (CCDs) are opticalcircuit components for utilization with light signals and representingthe light signals as digital signals. CISs and CCDs are used in theprior art. These two components are widely applied to many devices,including scanners, video cameras, and digital still cameras. CCDs useis limited in the market due to price and the volume considerations. Asa result, CISs enjoy greater popularity in the market.

Since a CMOS image sensor device is produced using conventionalsemiconductor techniques, the CMOS image sensor has advantages of lowcost and reduced device size. The CMOS image sensor is applied indigital electrical products including personal computer cameras anddigital cameras and may be classified into a linear type and a planetype. The linear CMOS is often used in scanners and the plane CMOS isoften used in digital cameras.

Please refer to FIG. 1 showing a cross-sectional diagram of aconventional CMOS image sensor 100. The image sensor 100 comprises apixel array region 102, an optical black region 104, and a logic region106, respectively formed on a semiconductor substrate 110. Thesemiconductor substrate 110 comprises a plurality of shallow trenchisolations 112 and a plurality of photodiodes 114. Each photodiode 114electrically connects with at least one corresponding MOS transistor(not shown). The shallow trench isolation 112 is used as an insulatorbetween any two adjacent photodiodes 114.

A planarized layer 116 is formed over the semiconductor substrate 100 tocover the photodiodes 114 and the shallow trench isolations 112.Patterned metal layers 118, 120, and 122 are formed on the planarizedlayer 116. A planarized layer 124 is formed on the patterned metallayers. The planarized layer 124 may have a multilayer structurecomposed of, for example, a HDP layer (a silicon oxide layer formed by ahigh density plasma process) and a PETEOS layer (a silicon oxide layerformed from tetraethyl ortho silicate by a plasma enhanced chemicalvapor deposition process). A passivation layer 130 is formed on theplanarized layer 124 to prevent water vapor from entering the devicesection. A cap oxide layer 132 may be further deposited on thepassivation layer 130.

Thereafter, a color filter array (CFA) 134 comprising a plurality ofred, green, and blue (R/G/B) light filter patterns are formed on the capoxide layer 132 in the pixel array region 102. A black layer 136 ispositioned on the cap oxide layer 132 in the optical black region 104. Aplanarized layer 138 is formed on and between the CFA and the blacklayer. A plurality of microlenses 140 are formed on the cap oxide layer138. A cap oxide layer 142 is disposed on the top to protect themicrolenses 140. The metal layer 122 in the logic region 106 is exposedto the ambient air to serve as a pad for electric connection.

However, during the manufacturing process of a conventional CMOS imagesensor, after the passivation layer 130 is formed, the photodiodes oftenhave plenty of dangling bonds on the surface, leading to a currentleakage (that is, dark current) problem. A conventional technique usinga hydrogen annealing process is performed to solve the problem, as shownin FIG. 2 indicating an annealing step 131. However, a patterned metallayer 120 for light shielding contains metal atoms which may react withthe hydrogen, and as a result, the removal of dangling bonds is impededby the metal layer 120. Thus, a high dark current occurs.

Therefore, novel image sensor devices or manufacturing methods thereofare needed to solve the dark current problem.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a manufacturing methodof an image sensor device to manufacture an image sensor device havingan improved dark current, as well as excellent light shieldingproperties in the optical black region.

Another object of the present invention is to provide an image sensordevice having a relatively low dark current while still having goodlight shielding properties in the optical black region.

The method of manufacturing an image sensor device according to thepresent invention comprises the steps as follows. First, a semiconductorsubstrate is provided. The semiconductor substrate comprises a pixelarray region, a logic region, and an optical black region between thepixel array region and the logic region. The pixel array regioncomprises a photo sensing unit array and a plurality of isolationstructures for isolating each of the photo-sensing units. Subsequently,a first planarized layer is formed over the semiconductor substrate tocover the photo-sensing units. A patterned metal layer is formed overthe first planarized layer in the pixel array region and the logicregion. A second planarized layer is formed over the semiconductorsubstrate to cover the patterned metal layer. An optical black layer isformed over the second planarized layer in the optical black region at atemperature less than 400° C. A color filter array is formed on thesecond planarized layer in the pixel array region. A third planarizedlayer is formed on the optical black layer and the color filter array. Aplurality of microlenses is formed on the third planarized layer,wherein the microlenses are positioned correspondingly over the colorfilter array. Finally, each layer over the metal layer in the logicregion is removed to expose the metal layer in the logic region to serveas a pad.

The image sensor device according to the present invention comprises asemiconductor substrate, a pixel array region, a logic region, and anoptical black region. The pixel array region is on the semiconductorsubstrate and comprises a photo sensing unit array. The logic region ison the semiconductor substrate and comprises a peripheral circuit. Theoptical black region is positioned between the pixel array region andthe logic region on the semiconductor substrate and comprises aphoto-sensing unit on the semiconductor substrate, a first planarizedlayer on the photo sensing unit, a second planarized layer on the firstplanarized layer, and an optical black layer on the second planarizedlayer.

In the method of manufacturing an image sensor device according to thepresent invention, a light-shielding metal layer as conventionally usedin the optical black region is not formed, and instead, an optical blacklayer comprising metal having has good light shielding properties isformed after a passivation layer is formed and before a color filterarray is formed. Therefore, in the dangling bond passivation process byannealing, the passivation of the dangling bonds in the optical blackregion is more efficient without impedance by a conventional lightshielding metal layer. Thereafter, an optical black layer can be formedfrom a material comprising metal at a relatively low temperature, and animage sensor device having an improved dark current can be obtained.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional diagram showing a conventional CMOS imagesensor;

FIG. 2 shows a conventional hydrogen annealing process performed duringa conventional manufacturing process of a CMOS image sensor;

FIG. 3 shows an image sensor device according to the present invention;

FIGS. 4 to 9 show the manufacturing method of the image sensor deviceaccording to the present invention; and

FIGS. 10 to 21 show a result of measuring a dark current on variouslocations of the image sensor device.

DETAILED DESCRIPTION

Please refer to FIG. 3 showing an image sensor device 200 according tothe present invention. The image sensor device 200 comprises asemiconductor substrate 210, a pixel array region 202, a logic region206, and an optical black region 204. The pixel array region 202 is onthe semiconductor substrate 210 and comprises a photo sensing unit array214. The logic region 206 is on the semiconductor substrate 210 andcomprises a peripheral circuit. The optical black region 204 ispositioned between the pixel array region 202 and the logic region 206on the semiconductor substrate and comprises a photo sensing unit 215 onthe semiconductor substrate 210, a first planarized layer 216 on thephoto sensing unit 215, a second planarized layer 224 on the firstplanarized layer 216, and a optical black layer 236 on the secondplanarized layer 224.

It is noted that the optical black layer 236 comprises a metal layerformed at a low temperature, for example less than 400° C. The metallayer may comprise titanium, or a combination of titanium and titaniumnitride.

The photo sensing unit array 214 may comprise a photodiodecorrespondingly electrically connecting to at least one MOS transistor.The pixel array region 202 comprises, in addition to the photo sensingunit array 214, a plurality of isolation structures 212 used to isolateeach of the photo sensing units, a planarized layer (which may be thefirst planarized layer 216 mentioned above) covering the photo sensingunit array 214 and the isolation structures 212, a patterned metal layer218 as a light shielding layer on the planarized layer for lightshielding, another planarized layer (may be a multilayer structure, suchas the second planarized layer 224 mentioned above) on the patternedmetal layer 218 on the first planarized layer, a color filter array 234on the planarized layer corresponding to the photo sensing unit array214, and a microlens array 240 on the color filter array 234.

The logic region 206 comprises an isolation layer 213, a planarizedlayer on the isolation layer 213, and a patterned metal layer 222 on theplanarized layer. The planarized layer may be the first planarized layer216 mentioned above.

Referring to FIGS. 4-9, the image sensor device 200 may be manufacturedby the method described hereinafter. First, a semiconductor substrate210 is provided. The semiconductor substrate 210 comprises a pixel arrayregion 102, a logic region 106, and an optical black region 104 betweenthe pixel array region and the logic region. The pixel array region 102comprises a photo sensing unit array 214 and a plurality of isolationstructures 212 for isolating each of the photo-sensing units. Aphoto-sensing unit 215 is on the semiconductor substrate 210 in theoptical black region 104. An isolation layer 213 is on the semiconductorsubstrate 210 in the logic region 106. The planarized layer 216 isformed on the semiconductor substrate 210 to cover each photo-sensingunit. The planarized layer may be formed through forming a dielectriclayer by a deposition method and planarizing the dielectric layer by,for example, a chemical mechanical polishing process.

Next, referring to FIG. 5, patterned metal layers 218 and 222 are formedover the planarized layer 216 in the pixel array region 102 and thelogic region 106. The patterned metal layer 218 serves as alight-shielding layer. The patterned metal layer 222 serves as a pad.The patterned metal layers 218 and 222 may be formed through forming ametal layer by sputtering and forming the pattern by etching process.

Referring to FIG. 6, a planarized layer 224 is formed over thesemiconductor substrate 210 to cover the patterned metal layers 218 and222. The planarized layer may comprise dielectric material, and may bein a single or multi-layer structure. For example, the planarized layermay be formed through subsequently forming a HDP layer 226 and a PETEOS228 and planarizing the top of the PETEOS layer 228. The passivationlayer 230, such as a plasma enhanced-SiN layer, may be further formed onthe planarized layer 224.

Referring to FIG. 7, after the processes as mentioned above areperformed, dangling bonds, such as —Si—, and —Si—O—, etc., tend to beproduced on the surface of the photodiode in the photo-sensing units 214and 215. The dangling bonds facilitate an occurrence of dark current,and thus the measurement for light intensity is affected, that is, thesensing sensitivity for the photodiode is affected. Thus, an annealing231 with hydrogen or other hydrogen-containing substance may beperformed to allow the hydrogen molecules or atoms to be incorporatedinto the planarized layer and reach the surface of the photodiode toreact with the dangling bonds for passivating the dangling bonds. It isnoted that, in the conventional technique, when the annealing process isperformed, part of the hydrogen molecules or atoms may react with metalin the metal light shielding layer having a large area located in theoptical black region, and the movement of hydrogen molecules or atoms tothe underneath photodiode surface is impeded. Accordingly, the resultingimage sensor device still has a high dark current occurring in theoptical black region. However, in the present invention, no metal lightshielding layer is located over the photo sensing unit in the opticalblack region during the annealing process, and thus the reaction of themetal with the hydrogen molecules or atoms will not take place, suchthat most hydrogen can move to the surface of the photodiode, leading amore efficient passivation of the dangling bonds. Thus, the problem ofdark current can be improved.

Referring to FIG. 8, an oxide layer 232, such as a plasma enhanced oxidelayer, may be further formed on the passivation layer 230 after theannealing to recover the surface chemical structure of the passivationlayer 230, but it is not a requisite. Next, an optical black layer 236may be formed on the oxide layer in the optical black region. Theoptical black layer 236 is formed through metal sputtering process at atemperature less than 400° C. to form a low temperature metal layer. Anymetal material can be formed into a film by low temperature sputteringcan be used as the optical black layer of the present invention, such astitanium or the combination of titanium and titanium nitride. Then, acap oxide layer 244 may be formed over the semiconductor substrate 210to cover the optical black layer 236. The cap oxide layer 244 may beformed at a low temperature and may comprise a plasma enhanced oxidelayer to recover the damaged surface in previous processes, such assputtering, and provide protection.

Referring to FIG. 9, a color filter array 234 is formed on theplanarized layer 224 or the cap oxide layer 244 (if formed) in the pixelarray region, that is, a red light filter array, a green light filterarray, and a blue light filter array are sequentially formed over thecorresponding photodiodes. Thereafter, a planarized layer 238 is formedover the color filter array 234 and part of the optical black layer 236.Thereafter, a plurality of microlenses are formed on the planarizedlayer 238 at the position corresponding to the color filter array 234.The microlenses may be formed through forming a polymeric layer (notshown) from an acrylate material, and performing an exposure, adevelopment, and a reflow process on the polymeric layer. A planarizedlayer, such as cap oxide layer 242, may be further formed over the colorfilter array and in the optical black region for surface protection.

Finally, each layer, such as the planarized layer 224, the passivationlayer 230, the oxide layer 232, and the cap oxide layers 244 and 242,over the patterned metal layer 222 as a pad in the logic region 206 maybe removed using for example an etching process to expose the patternedmetal layer 222 in the logic region 206 to serve as a pad for electricconnection. Thus, an image sensor device according to the presentinvention can be accomplished.

Alternatively, the step of removing each layer over the patterned metallayer 222 in the logic region 206 may be performed after forming theplanarized layer 224 or the passivation layer 230 to remove theplanarized layer 224 or the passivation layer 230 by for example maskand etching processes. Finally, after the cap oxide layer 242 is formed,each layer over the patterned metal layer 222 is removed again to reopenthe patterned metal layer as a pad.

It is noted that steps after the annealing process for dangling bondpassivation are preferably performed at a low temperature less than theannealing temperature, such as 400° C., to avoid spoiling the danglingbond passivation performed in the previous process.

The image sensor device obtained by the method of the present inventionhas a relatively low dark current. Please refer to FIGS. 10-21, showinga result for measuring dark current produced at various positions of theimage sensor device. The ordinate is dark current represented byelectrons per second. The abscissa is the column number of the imagesensor device.

FIGS. 10-13 respectively show the measurement result of dark current atthe pixel array region, the optical black region at the right end of thepixel array region, the optical black region at the bottom of the pixelarray region, and the optical black region in the right bottom corner ofthe device of a conventional image sensor device. The image sensordevice uses a metal light shielding layer in the optical black regionand an hydrogen annealing was performed at a flow ratio ofhydrogen:nitrogen=0.8:20 to passivate dangling bonds after the metallight shielding layer was formed during the manufacturing. The curvesshown in FIGS. 10 and 12 arise significantly in two ends, indicatingthat the dark current at the edge part is high. The curves shown inFIGS. 11 and 13 indicate that the dark current in the optical blackregion is very high, and there is a significant difference between thedark current in the pixel array region and the dark current in theoptical black region.

FIGS. 14-17 respectively show the measurement result of dark current atthe pixel array region, the optical black region at the right end of thepixel array region, the optical black region at the bottom of the pixelarray region, and the optical black region in the right bottom corner ofthe device of a conventional image sensor device. The image sensordevice uses a metal light shielding layer in the optical black regionand an hydrogen annealing was performed at a flow ratio ofhydrogen:nitrogen=2:20 to passivate dangling bonds after the metal lightshielding layer was formed during the manufacturing. The curves shown inFIGS. 14 and 16 arise significantly in two ends, indicating that thedark current at the edge part is high. The curves shown in FIGS. 15 and17 indicate that the dark current in the optical black region is high tobe about 2000 to 4000 e/s, and there is a significant difference betweenthe dark current in the pixel array region and the dark current in theoptical black region.

FIGS. 18-21 respectively show the result of measuring dark current atthe pixel array region, the optical black region at the right end of thepixel array region, the optical black region at the bottom of the pixelarray region, and the optical black region in the right bottom corner ofthe device of an image sensor device according to the present invention.During the manufacturing, a hydrogen annealing was performed at a flowratio of hydrogen:nitrogen=2:20 to passivate dangling bonds without ametal light shielding layer presenting in the optical black region, andthus more dangling bonds could be passivated. The dark current shown inFIGS. 18-20 is significantly lower than that in the conventionaltechniques. The curves shown in FIGS. 18 and 20 do not arisesignificantly at two ends, indicating that there is almost no differencebetween the dark current at the edge part and the dark current at theinterior part. As shown in FIGS. 19 to 21, the dark current in theoptical black region is reduced to be about 1000 to 2000 e/s, and thedifference between the dark current in the pixel array region and thedark current in the optical black region is decreased, indicating theimage sensor device made by the method of the present invention has animproved dark current.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

1. An image sensor device, comprising: a semiconductor substrate; apixel array region on the semiconductor substrate, the pixel arrayregion comprising a photo sensing unit array; a logic region on thesemiconductor substrate, the logic region comprising a peripheralcircuit; and an optical black region between the pixel array region andthe logic region on the semiconductor substrate, the optical blackregion comprising a photo sensing unit on the semiconductor substrate, afirst planarized layer on the photo sensing unit, a second planarizedlayer on the first planarized layer, and a optical black layer on thesecond planarized layer.
 2. The image sensor device of claim 1, whereinthe optical black layer comprises a metal layer formed at a temperatureless than 400° C.
 3. The image sensor device of claim 2, wherein themetal layer comprises titanium.
 4. The pixel array region of claim 2,wherein the metal layer comprises titanium and titanium nitride.
 5. Theimage sensor device of claim 1, wherein the photo sensing unit arraycomprises a plurality of photodiodes.
 6. The image sensor device ofclaim 1, further comprising a color filter array correspondingly overthe photo sensing unit array in the pixel array region.
 7. The imagesensor device of claim 1, wherein the second planarized layer comprisesa plurality of dielectric layers.
 8. The image sensor device of claim 1,further comprising a passivation layer over the second planarized layer.9. The image sensor device of claim 1, further comprising a cap oxidelayer over the optical black layer.